*Excludes Observations that spanned multiple years
| Pre 1970 | 5 |
|---|---|
| 1970 | 1 |
| 1971 | 5 |
| 1972 | 4 |
| 1973 | 0 |
| 1974 | 0 |
| 1975 | 1 |
| 1976 | 0 |
| 1977 | 0 |
| 1978 | 1 |
| 1979 | 2 |
| 1980 | 0 |
| 1981 | 0 |
| 1982 | 5 |
| 1983 | 1 |
| 1984 | 0 |
| 1985 | 45 |
| 1986 | 77 |
| 1987 | 120 |
| 1988 | 203 |
| 1989 | 65 |
| 1990 | 68 |
| 1991 | 215 |
| 1992 | 112 |
| 1993 | 196 |
| 1994 | 273 |
| 1995 | 306 |
| 1996 | 211 |
| 1997 | 220 |
| 1998 | 35 |
| 1999 | 42 |
| 2000 | 33 |
| 2001 | 93 |
| 2002 | 25 |
| 2003 | 92 |
| 2004 | 100 |
| 2005 | 70 |
| 2006 | 38 |
| 2007 | 66 |
| 2008 | 60 |
| 2009 | 64 |
| 2010 | 85 |
| 2011 | 63 |
| 2012 | 101 |
| 2013 | 112 |
| 2014 | 89 |
| 2015 | 89 |
| 2016 | 79 |
| 2017 | 82 |
| 2018 | 45 |
| 2019 | 111 |
| 2020 | 39 |
| 2021 | 118 |
| 2022 | 62 |
| 2023 | 31 |
| 2024 | 45 |
| 2025 | 8 |
| Total | 4013 |